Field of the Invention
The present invention relates to flow velocimeter systems.
Description of the Related Art
Known flow velocimetry includes a particle image velocimeter (hereinafter called a PIV) that is configured to irradiate small particles mixed in fluid with light such as laser light to acquire an image of scattered light therefrom, thus finding a moving distance of a particle or a group of particles from images of particles acquired at slightly different times and so measuring the velocity of fluid (flow velocity) in the two-dimensional plane.
In the velocity field of the PIV, vectors (noise) having a very large error are present. Such noise is generated because particles flow out from or into a light sheet due to the velocity component perpendicular to the light sheet or the voracity component, thus failing to find a correlation between the images. Such generation of the noise cannot be avoided, meaning that the velocity obtained includes a very large error.
To solve such a problem, Japanese Patent Application Laid-Open No. 2004-20385 (Patent Document 1) proposes a technique of performing Fourier transformation of a time-series velocity at each velocity defining point in flow velocity vector distributions acquired from two images that are temporally continuous, to which cutoff filtering or low-pass filtering is applied in the frequency space for inverse Fourier transformation, thus obtaining a final time-series velocity of the fluid.